Commuters will start receiving phone and internet coverage in some of Sydney's train tunnels this week — 16 years after Optus first offered to carry out the work.

The telco is the lead carrier in a project to lay 10km of cabling on the North Shore and Western train lines so that mobile, laptop and tablet users no longer suffer regular network drop-outs.

But it's been a long time coming.

NSW Transport Minister Gladys Berejiklian said that Optus first approached the state government in 1996, offering to do the work.

She blamed the previous Labor administration for failing to take up the offer. "It is ridiculous it has taken this long.

"We have listened to the feedback and this is another win for customers who have for so many years been frustrated with the lack of coverage in tunnels."

Berejiklian said that Optus and Telstra customers will get coverage between Central and Chatswood stations later this week.

Vodafone customers will get reception in tunnels at a later date.

Network cabling will be laid in the City Circle and Eastern Suburbs lines in future.

Optus' networks managing director Gunther Ottendorfer said that the new network infrastructure was activated on Sunday night, after a period of testing.

"Today marks an important step in delivering much-needed rail-tunnel coverage to Sydneysiders," he said in a statement.

Optus has also been looking to improve network coverage for its customers in buildings using the 900MHz spectrum, which it had previously used for 2G.

In addition, Optus had plans to introduce 500 more mobile sites into its network, and to upgrade the infrastructure of around 2500 of its existing sites. The telco also announced that HSPA+ services will be made available at over 700 sites across Australia.

"Optus is currently rolling out one of Australia's largest network enhancements, delivering stronger 3G coverage across regional centres and major capital cities, including Sydney, Melbourne, Darwin, Brisbane and Perth. As a result, our customers are experiencing better in-building coverage, stronger 3G signals and faster data speeds in more places," the company said today.